The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Substrate processing systems may be used to deposit, etch or treat film on a substrate such as a semiconductor wafer. The substrate processing systems typically include a processing chamber, a gas distribution device and a substrate support. During processing, the substrate is arranged on the substrate support. Different gas mixtures may be introduced into the processing chamber to treat the film. Substrate heating and/or radio frequency (RF) plasma may also be used to activate chemical reactions.
The substrate may be processed by two or more semiconductor tools and may be exposed to air between processing steps. Alternatively, the substrate may be exposed to oxidizing gases such as molecular oxygen (O2) or water (H2O) during processing in single tool.
Cobalt (Co) will likely be used for processes with less than 10 nm feature sizes. For example, Co may be used for logic interconnects (e.g. middle-of-the-line (MOL) or back-end-of-line (BEOL)), metal gates, and/or source/drain contacts. There are a number of process issues with using Co as a metal layer in these applications. Other than Co, other metals such as tungsten (W), nickel (Ni), rhodium (Rh), and ruthenium (Ru) also can be used for metal gates and/or source/drain contacts. Copper (Cu), W, Ni, Rh, and Ru can be used for logic interconnects (e.g. middle-of-the-line (MOL) or back-end-of-line (BEOL)).
A barrier layer is deposited between the metal layer and underlying layers to prevent diffusion. The barrier layer includes titanium/titanium nitride (Ti/TiN), tantalum nitride/tantalum (TaN/Ta), TiN or TaN may be oxidized after exposure to air or oxidizing chemistry. Co or other metals may not adhere well to oxidized barrier layers. As a result, the surface of the barrier layer needs to be cleaned before the metallization step to reduce defects and other integration issues related to adhesion.
For resistivity reduction and grain growth, the Co and metal layer is typically annealed to about 400° C. post deposition. Co undergoes phase transformation during annealing, which leads to the development of a large stress hysteresis within the film. The stress hysteresis can cause film delamination if adhesion of the Co film is inadequate. Other metals also experience stress hysteresis and some phase transformation which could lead to adhesion issue as well.